数据库表数据
CREATE TABLE `food_new` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`code` varchar(255) DEFAULT NULL COMMENT '物料编码',
`name` varchar(255) NOT NULL COMMENT '物料名称',
`type` varchar(255) DEFAULT NULL COMMENT '规格型号',
`unit` varchar(255) DEFAULT NULL COMMENT '单位',
`price` double(10,2) DEFAULT NULL COMMENT '单价',
`category` varchar(255) DEFAULT NULL COMMENT '所属类别',
`sort` varchar(4) DEFAULT NULL COMMENT '排序',
`create_time` datetime DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP COMMENT '创建时间',
`update_time` datetime DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP COMMENT '修改时间',
PRIMARY KEY (`id`) USING BTREE,
UNIQUE KEY `name` (`name`) USING BTREE
) ENGINE=InnoDB AUTO_INCREMENT=819 DEFAULT CHARSET=utf8mb4 ROW_FORMAT=DYNAMIC; 假设，我们现在需要将数据库中的`name`和`category`字段分别映射为`key`和`value`。本案例是以非web项目来演示。
mybatis配置文件
SqlMapConfig.xml文件内容：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//ibatis.apache.org//DTD Config 3.0//EN"
"http://ibatis.apache.org/dtd/ibatis-3-config.dtd">
<configuration>
<environments default="environment">
<environment id="environment">
<transactionManager type="JDBC" />
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf8&useSSL=false" />
<property name="username" value="root"/>
<property name="password" value="123123"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="mappers/FoodMapper.xml" />
</mappers>
</configuration>
mybatis的xml文件
FoodMapper.xml文件内容：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//ibatis.apache.org//DTD Mapper 3.0//EN"
"http://ibatis.apache.org/dtd/ibatis-3-mapper.dtd">
<mapper namespace="com.test.dao.FoodDao">
<resultMap id="name_category" type="java.util.HashMap">
<result property="key" column="name" />
<result property="value" column="category" />
</resultMap>
<select id="findNameCategoryMap" parameterType="java.util.Map" resultMap="name_category">
select name,category from food_new
</select>
</mapper>
mybatis的工具类-与数据库建立连接
package com.test.utils;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
public class MyBatisUtil {
private static SqlSessionFactory sf;
static {
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
sf = builder.build(MyBatisUtil.class.getClassLoader().getResourceAsStream("SqlMapConfig.xml"));
}
public static SqlSession getSession() {
return sf.openSession();
}
public static void main(String[] args) {
SqlSession session = MyBatisUtil.getSession();
System.out.println(session);
session.close();
}
}
dao
package com.test.dao;
import java.util.Map;
public interface FoodDao {
Map<String, String> findNameCategoryMap();
}
自定义查找结果集–实现ResultHandler接口
ResultHandler,顾名思义,对返回的结果进行处理,最终得到自己想要的数据格式或类型。也就是说,可以自定义返回类型。
package com.test.config;
import java.util.HashMap;
import java.util.Map;
import org.apache.ibatis.session.ResultContext;
import org.apache.ibatis.session.ResultHandler;
public class NameCategoryMapResultHandler implements ResultHandler {
private final Map<String, String> name_Category_Map = new HashMap<String, String>();
@Override
public void handleResult(ResultContext context) {
@SuppressWarnings("unchecked")
Map<String, String> map = (Map<String, String>) context.getResultObject();
name_Category_Map.put(map.get("key"), map.get("value"));
}
public Map<String, String> getMappedResults() {
return name_Category_Map;
}
}
service
package com.test.service;
import java.util.Map;
public interface FoodService {
Map<String, String> findNameCategoryMap();
}
实现：
package com.test.service.impl;
import java.util.Map;
import org.apache.ibatis.session.SqlSession;
import com.zhuoshan.config.NameCategoryMapResultHandler;
import com.zhuoshan.config.NameSortMapResultHandler;
import com.zhuoshan.service.FoodService;
import com.zhuoshan.utils.MyBatisUtil;
public class FoodServiceImpl implements FoodService {
private SqlSession session = MyBatisUtil.getSession();
@Override
public Map<String, String> findNameCategoryMap() {
NameCategoryMapResultHandler handler = new NameCategoryMapResultHandler();
session.select("com.test.dao.FoodDao.findNameCategoryMap", handler);
return handler.getMappedResults();
}
public static void main(String[] args) {
FoodServiceImpl f = new FoodServiceImpl();
System.out.println(f.findNameCategoryMap());
System.out.println(f.findNameCategoryMap().size());
}
}
调用
package com.test.core;
import java.util.Map;
import com.zhuoshan.service.FoodService;
import com.zhuoshan.service.impl.FoodServiceImpl;
public class FoodMain {
public static void main(String[] args) throws Exception {
FoodService foodService = new FoodServiceImpl();
Map<String, String> name_category_map = foodService.findNameCategoryMap();
name_category_map.forEach((key, value) -> System.out.println(key + ":" + value));
}
}